Establishing a Function to assign Role to Windows Authentication User

I am having issues learning how to establish a Roles Function within this code that will assigned all Windows Authentication Users to a Role that is located in my SQL Database Table. 

This is what I have so far. 

namespace TMC
{
    public class TMCUser
    {
        public int UserId { get; set; }
        public string Name { get; set; }
        public string UserName { get; set; }
        public string RoleName { get; set; }
        public Boolean IsActive { get; set; }

        Connection Conn = new Connection();
        public TMCUser()
        {

        }

        public TMCUser(string userName)
        {
            using (SqlConnection conn = Conn.GetUtilitiesConnection)
            using (SqlCommand cmd = new SqlCommand("HBCC.usp_SelActiveUser", conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.Add("@UserName", SqlDbType.NVarChar).Value = userName.Split('\\')[1];
                if (conn.State != ConnectionState.Open)
                    conn.Open();
                SqlDataReader dr = cmd.ExecuteReader();

                if (dr.Read())
                {
                    UserId = (int)dr["UserId"];
                    Name = (string)dr["Name"];
                    UserName = (string)dr["UserName"];
                    RoleName = (string)dr["RoleName"];
                    IsActive = (bool)dr["IsActive"];
                }
                conn.Close();
            }
        }

        public Boolean AddUser()
        {
            return true;
        }

        public Boolean DisAbleUser(int userid)
        {
            return true;
        }

        // CREATE ROLE FUNCTION
	public TMCUser(string RoleName)
	{


	}
			

     
    }